Communication systems are known to include a plurality of subscribers and supporting infrastructure. For wireless communication systems, the plurality of subscriber units may be cellular telephones, mobile radios, portable radios, wireless personal digital assistants, personal computers equipped with a wireless modem, or any other device that receives and/or transmits information via a wireless RF communication path. The supporting infrastructure for a wireless communication system includes a system controller, a plurality of base station controllers, and a plurality of base stations. For terrestrial wireless communication systems, the plurality of base stations is distributed throughout a geographic region. Groups of the base stations are coupled to a base station controller wherein the base station controller provides control functionality for the group of base stations. Groups of base station controllers are coupled to the system controller wherein the system controller controls the overall functionality of the terrestrial communication system.
In satellite communication systems, the base stations are located on a satellite that orbits the earth. Each satellite may function as a plurality of base stations and base station controller, which communicate with a satellite system controller that is on the ground. Satellite communication systems are designed for supporting communications between subscribers located anywhere in the world. In contrast, terrestrial wireless communication systems generally provide services for subscribers within a geographical location. Such a geographical location may be limited to a town, city, county, state, and/or country and/or continent. Of the terrestrial communication systems there are two basic types, cellular and land mobile (or two-way). A cellular wireless communication system provides one-to-one communications for its subscribers, while a land mobile communication system provides one to many, many to one, and one to one communications for its subscribers.
There are two types of land mobile wireless systems, public wireless systems and private wireless systems. A public land mobile wireless system is operated by an independent entity that sells time on the wireless system to a plurality of subscribers. As such, a service provider would sell airtime to subscribers such as taxicab companies, trucking companies, delivery companies, etc. Private wireless communication systems, however, are owned and operated by the same entity. As such, subscribers do not pay to utilize the wireless system.
As is known, land mobile two-way communication systems provide dispatch services by providing a dispatch overlay. This allows inbound voice packets from a single control access transmission unit (e.g., a dispatcher) to be routed to a packet switch and a packet duplicator where the packet duplicator generates N copies of the inbound voice packets. The N copies are sent to base station transmitter sites where the wireless links are used to carry the repeated voice packets to targeted subscribers. This approach provides fast one to many half-duplex communications, but currently only provides such services for like subscribers, i.e., subscribers of the same communication system.
As is also known, a land mobile wireless communication system provides seamless wireless communications within its coverage area. To extend the coverage area of a single system, communication systems are linked together such that subscribers may roam from one system to another and continue to receive seamless wireless services. Typically, to establish the link between the two communication systems, a high data rate transmission link is established, such as a T1 link, microwave link, etc. Such linking is usually done between public land mobile systems, where each system provider collects revenue when a subscriber of another system utilizes its communication resources. To further extend wireless services to subscribers in non-coverage areas of a public system, or public system network, the public systems may obtain resources from private systems. Thus, when a communication is occurring between subscribers in a private system and subscribers in a public system, a conference bridge is established. The conference bridge sums the transmissions generated by the subscribers, which must include a high quality audio vocoder (e.g., 13 kbps). In most communication systems, subscribers include a lower quality audio vocoder (e.g., in the range of 2 kbps to 4 kbps).
As an alternative to establishing a conference bridge between communication systems, a communication system gateway may be utilized. The gateway maps the IDs of subscribers from one communication system to another. The gateway evokes the mapping and facilitates allocation of RF communication resources in both systems when it receives a call request. Once the resources have been allocated, the gateway facilitates the call by replicating the transmissions of both systems and providing them to the other system. While this method works well to process communications between different systems, it has a centralized replication of communications which for some communication systems, such as SMARTZONE and IDEN systems by Motorola, Inc., perform the replication within their own networks. As such, the replication is redundant.
While the above techniques provide extended coverage areas for subscriber units beyond their own communication system, there are still geographic areas in which terrestrial systems do not provide services. Such geographical areas are typically low in population density such that establishing a complete wireless communication system is cost prohibitive. In these areas, a subscriber is only able to subscribe to a satellite communication system such as an IRIDIUM Satellite Communication System. The IRIDIUM system teaches the use of a global coverage satellite system as fill-in for spotty terrestrial cellular systems. It uses dual mode subscriber radios and its HLR ("Home Location Register") concept allows for one number calling anywhere, even if the user/unit is in the coverage area of a lower cost per unit of air time terrestrial system. This scheme is for individual one-to-one calls only and it utilizes GSM mapping protocols. It, however, does not support instant access calls to satellite units nor to terrestrial two-way wireless land mobile systems.
Therefore, a need exists for a method and apparatus that extends two-way land mobile communication services into remote geographic areas that are not covered by terrestrial communication systems by linking terrestrial communication systems with satellite communication systems.